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.4 Bar, Need Help Diagnosing

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Need some help. Trying to diagnose why I cannot boost more than .4 bar. Have a 2005 Turbo S with 17k miles, FVD Exhaust, 100 cell cats, FVD Headers, EVOMS DV and FVD Flash. I am don't drive the car too much maybe 3000 miles a year (hoping to get this number much higher once I resolve this).

Here is what has been eliminated:

No codes apparent (checked with Durametric and PIWIS)

No Boost Leak, smoke and pressure tested no leaks anywhere

DVs hold vacuum properly

Stock Wastegates open at close properly

After eliminating the above we thought it might be that I had some bad fuel in the car and might be detecting some knocking. So I ran the tank to completely empty and put in some fresh 93. Immediately upon driving, the car was back to boosting .8 to 1 bar (have an FVD flash). Great we thought so we call it a night.

Did not drive the next day, but I hopped in the car tonight and its back to boosting .4 bar.

Any ideas??????

Possible Culprits:

-Bad Maf Sensor

-Bad Knock Sensor

-Bad ECU Flash

-Maybe a fuel pump starting to fail?

What do you guys think? Any suggestions on how to diagnose?

Help would be MUCH appreciated!!!

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Have you done a boost leak test?

Have you data logged with the Durametric cable (if you have one)?

Could be N75 valve is bad...

Is odd that adding good fuel fixed it for a bit, but it may not be the good fuel as much as it was stirring the tank...fuel filter?

You physically checked both waste gate actuators, arms, and the waste gate flaps to make sure they're not binding up or have some other problem. Waste gate flaps should be pulled towards the front of the car to be fully seated closed. If one is stuck open or a rod has gotten stuck (most likely to happen on psgr side turbo) and can't suck back into the actuator it would limit boost big time.

Just thoughts...

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Your going to have to do some data logging in that case.

I am really surprised you don't have some codes. So you need to have a look at your: Set boost,IAT's, Ignition angle, Maf data, rpm, O2 pre cat 1 and 2 (to work out AFR).

Do some pulls in 3rd form 2000 to 6000 rpm and see what you get. Your garage that has done all the checking so far should be able to interpret the data. I'm sure better than me on here will also be able to as well.

i recon there are a few more items to data log but I just cant think of the atm. Hopefully some one who regularly data logs will come along.


Edited by Sunnyside
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